1. Field of the Invention
The present invention relates to a semiconductor device, a nonvolatile semiconductor memory device and process for the same, in particular, to a semiconductor device and a nonvolatile semiconductor memory device where it is possible to simplify the manufacturing processes thereof as well as those processes.
2. Description of the Background Art
Conventionally, a nonvolatile semiconductor memory device is known as one type of semiconductor devices. FIG. 15 is a schematic cross section view showing a conventional nonvolatile semiconductor memory device. Referring to FIG. 15, the conventional nonvolatile semiconductor memory device is described.
Referring to FIG. 15, the nonvolatile semiconductor memory device includes a memory cell region and a peripheral circuit region. In the memory cell region, shown in FIG. 15, a cross section view A showing a region where a plurality of memory cells are formed and a cross section view B which is a cross section view along the line Bxe2x80x94B in the above cross section view A are shown. Cross section view A is a cross section view in the bit line direction (direction approximately parallel to the direction in which interconnections 125a to 125c extend) in the memory cell region. Cross section view B is a cross section view in the word line direction (direction approximately perpendicular to the direction in which a phosphorous doped polysilicon film 116a to 116d extends as control gate electrodes) in the memory cell region.
In the memory cell region, an n well 105 is formed in a region at a predetermined depth from the main surface of a semiconductor substrate 101. A p well 111a is formed in a region located above the n well 105 in the semiconductor substrate 101. An element isolation insulating film 102a, 102b are formed on the main surface of the semiconductor substrate 101. As is seen from cross section views A and B, n type diffusion regions 120a to 120c are formed in the main surface of the semiconductor substrate 101 at predetermined intervals in the direction perpendicular to the surface of the paper in cross section view A. A silicon oxide film 112 is formed on the main surface of the semiconductor substrate 101. A polysilicon film 113ab, 113bb, 113cb which become floating gate electrodes is formed on the silicon oxide film 112. This polysilicon film 113ab, 113bb, 113cb as floating gate electrodes is formed of a plurality of pieces arranged at intervals in the direction perpendicular to the surface of the paper in cross section view A. That is to say, as shown in cross section view B, the pieces of polysilicon film 113ba, 113bb, 113bc, 113bd are arranged at intervals with interstitial regions wherein the n type diffusion regions 120a to 120c are formed. A three layered insulating film 115a to 115d is formed as an intermediate insulating film on the polysilicon film 113ab, 113bb, 113cb, 113ba, 113bc, 113bd as the floating gate electrodes. This three layered insulating film 115a to 115d is formed of a three layered structure of a silicon oxide film, a silicon nitride film and a silicon oxide film. A phosphorous doped polysilicon film 116a to 116d as control gate electrodes are formed on the above three layered insulating film 115a to 115d. A tungsten silicide (WSi) film 117a to 117d is formed on the phosphorous doped polysilicon film 116a to 116d. A silicon oxide film 118a to 118d are formed on the tungsten silicide film 117a to 117d. A boron phosphorous glass 123 is formed on the silicon oxide film 118a to 118d. Contact holes 124a to 124c are formed by partially removing portions of the boron phosphorous glass 123 and the silicon oxide film 112 in the regions located above the n type diffusion regions 120a to 120c. At the bottom of these contact holes 124a to 124c, the surfaces of the n type diffusion regions 120a to 120c are exposed. Interconnections 125a to 125c made of a conductive material are formed so as to extend from the inside of these contact holes 124a to 124c to the upper surface of the boron phosphorous glass 123. As for the material for these interconnections 125a to 125c, an aluminum-silicon-copper (Alxe2x80x94Sixe2x80x94Cu) alloy film can be used.
In cross section view B, of the memory cell region, the n type diffusion region 120a and the n type diffusion region (not shown) located on the left side of the above n type diffusion region 120a work as the source region and the drain region of one flash memory cell. These n type diffusion regions, the silicon oxide film 112, which works as a tunnel insulating film, the phosphorous doped polysilicon film 113ba as a floating gate electrode, the three layered insulating film 115a and the phosphorous doped polysilicon film 116a as a control gate electrode form one flash memory cell. In addition, the n type diffusion regions 120a, 120b as the source and drain regions, the silicon oxide film 112 which works as a tunnel insulating film, the phosphorous doped polysilicon film 113bb as a floating gate electrode, the three layered insulating film 115b and the phosphorous doped polysilicon film 116b as a control gate electrode form another flash memory cell. In addition, the n type diffusion regions 120b, 120c as the source and drain regions, the silicon oxide film 112 which works as a tunnel insulating film, the phosphorous doped polysilicon film 113bc as a floating gate electrode, the three layered insulating film 115c and the phosphorous doped polysilicon film 116c as a control gate electrode form another flash memory cell. Furthermore, the n type diffusion region 120c and an n type diffusion region (not shown) arranged on the right side of the n type diffusion region 120c with an interval between them as the source and drain regions, the silicon oxide film 112 which works as a tunnel insulating film, the phosphorous doped polysilicon film 113bd as a floating gate electrode, the three layered insulating film 115d and the phosphorous doped polysilicon film 116d as a control gate electrode form still another flash memory cell. The flash memory cells are arranged in a matrix form in the memory cell region.
In the peripheral circuit region of the nonvolatile semiconductor memory device shown in FIG. 15, an n type field effect transistor (FET) 126 and a p type FET 127 are formed. In the peripheral circuit region, an element isolation insulating film 102c is formed on the main surface of the semiconductor substrate 101. In the element formation region isolated by this element isolation insulating film 102c, a p well 111b is formed in the main surface of the semiconductor substrate 101 in the region where the n type FET 126 is formed. Then type diffusion regions 121a and 121b which become the source and drain regions of the n type FET 126 are formed with a channel region between them in the main surface of the semiconductor substrate 101 in this p well 111b. A silicon oxide film 129 is formed as a gate insulating film on the main surface of the semiconductor substrate 101. A phosphorous doped polysilicon film 116e is formed on the silicon oxide film 129 as a gate electrode in the region above the channel region located between the n type diffusion regions 121a and 121b which become the source and drain regions. A tungsten silicide film 117e is formed on the phosphorous doped polysilicon film 116e. A silicon oxide film 118e is formed on the tungsten silicide film 117e. 
In the region wherein the p type FET 127 is formed in the peripheral circuit region, an n well 108 is formed in the semiconductor substrate 101. P type diffusion regions 122a and 122b, which become the source and drain regions, are formed so as to face each other via a channel region in the main surface of the semiconductor substrate 101 in the above n well 108. A silicon oxide film 129 which becomes a gate insulating film is formed on the main surface of the semiconductor substrate 101. In the region which is located above the channel region and on the silicon oxide film 129, a phosphorous doped polysilicon film 116f is formed as a gate electrode. A tungsten silicide film 117f is formed on the phosphorous doped polysilicon film 116f. A silicon oxide film 118f is formed on the tungsten silicide film 117f. 
A boron phosphorous glass 123 is formed on the silicon oxide film 118e, 118f. Contact holes 124d to 124g are formed by partially removing the boron phosphorous glass 123 and the silicon oxide film 129 in the regions located above the n type diffusion regions 121a, 121b and the p type diffusion regions 122a, 122b. At the bottom of the contact holes 124d to 124g, respectively, the surface of the n type diffusion regions 121a, 121b and the p type diffusion regions 122a, 122b is exposed. Interconnections 125d to 125g made of a conductive film are formed so as to extend from the inside of the contact holes 124d to 124g to the upper surface of the boron phosphorous glass 123. As for the material of these interconnections 125d to 125g, an aluminum-silicon-copper (Alxe2x80x94Sixe2x80x94Cu) alloy film can be used.
FIGS. 16 to 27 are schematic cross section views for describing a manufacturing process of the conventional nonvolatile semiconductor memory device shown in FIG. 15. Referring to FIGS. 16 to 27, the manufacturing process of the conventional nonvolatile semiconductor memory device shown in FIG. 15 is described.
Here in FIGS. 16 to 27, basically the same cross sections as in FIG. 1 are shown. That is to say, cross section views positioned left side in FIGS. 2 to 8 and 10 to 14 show cross sections in the bit line direction of the memory cells while cross section views located in the middle show cross section views in the word line direction of the memory cells.
Firstly, as shown in FIG. 16, an element isolation insulating film 102a to 102c is formed in the region which becomes the memory cell region and in the region which becomes the peripheral circuit region in the main surface of a semiconductor substrate 101 which is a p type silicon substrate with the growth direction of  less than 100 greater than .
Next, a resist (not shown) is applied to the main surface of the semiconductor substrate 101. The resist lying above the memory cell region is removed through a photolithographic method. As a result, a resist film exists in the peripheral circuit region while the memory cell region converts to the condition wherein the main surface of the semiconductor substrate 101 is exposed. Then, phosphorous is injected (doped) into the semiconductor substrate 101 in the memory cell region by using the above resist film as a mask. An n well 105 (see FIG. 17) as the bottom well is formed through this phosphorous injection. As for the phosphorous injection conditions at this time, the conditions where the injection energy is 3 MeV and the injection concentration of phosphorous is 1.0xc3x971013/cm2 can be used. After this, the resist film is removed.
Next, a resist is applied to the main surface of the semiconductor substrate 101. Then, a resist film is formed above the memory cell region and above the regions where the n type FET 126 (see FIG. 15) is formed in the peripheral circuit region through a photolithographic method. At this time, in the region where the p type FET 127 (see FIG. 15) is formed in the peripheral circuit region, the main surface of the semiconductor substrate 101 is in an exposed condition. Then, phosphorous is injected into the semiconductor substrate 101 by using this resist film as a mask. An n well 108 is formed as shown in FIG. 17 through this phosphorous injection. As for the conditions of this phosphorous injection, the conditions where, for example, the injection energy is 1.2 MeV, the injection concentration of phosphorous is 1.0xc3x971013/cm2, and the like, can be used. In addition, following this phosphorous injection, phosphorous is injected to the semiconductor substrate 101 for a channel cut. As for the condition of the phosphorous injection for this channel cut, the conditions where, for example, the injection energy is 700 keV, the injection concentration is 3.0xc3x971012/cm2, and the like, can be used. In addition, boron may be injected into the semiconductor substrate 101 for counter doping. As for the boron injection conditions for this counter dopant, the conditions where, for example, the injection energy is 20 keV, the injection concentration is 1.5xc3x971012/cm2, and the like, can be used. After this, the resist film is removed.
Next, after applying the resist to the main surface of the semiconductor substrate 101, a resist film 109 is formed on the region where the p type FET 127 is formed in the peripheral circuit region as shown in FIG. 17 through a photolithographic method. At this time, in the memory cell region and in the region where an n type FET 126 is formed in the peripheral circuit region, the main surface of the semiconductor substrate 101 is in an exposed condition. Then, by injecting boron 110 into the semiconductor substrate 101 using the resist film 109 as a mask, p wells 111a, 111b (see FIG. 18) are formed. As for the conditions of this boron injection, the conditions where, for example, the injection energy is 700 ke V, the injection concentration is 1.0xc3x971013/cm2, and the like, can be used. In addition, boron for p channel cut may then be injected into the semiconductor substrate 101. As for the boron injection conditions for this p channel cut, the conditions where, for example, the injection energy is 270 keV, the injection concentration is 3.5xc3x971012/cm2, and the like, can be used. In addition, boron for channel doping may further be injected into the semiconductor substrate 101. As for the boron injection conditions for this channel doping, the conditions where, for example, the injection energy is 50 keV, the injection concentration is 1.2xc3x971012/cm2, and the like, can be used. After that, the resist film 109 is removed.
Next, as shown in FIG. 18, a silicon oxide film 112 is formed on the main surface of the semiconductor substrate 101 by using a thermal oxidation method. The film thickness of this silicon oxide film 112 is 10 nm. This silicon oxide film 112 works as a tunnel oxide film of a flash memory cell formed in the memory cell region.
Then, a phosphorous doped polysilicon film is formed on this silicon oxide film 112. This phosphorous doped polysilicon film can be formed by using a low pressure CVD (chemical vapor deposition) method. In addition, the film thickness of this phosphorous doped polysilicon film is 100 nm. A resist is applied to this phosphorous doped polysilicon film. Then, a resist film is formed on the phosphorous doped polysilicon film in the memory cell region and in the peripheral circuit region through a photolithographic method. By partially removing the phosphorous doped polysilicon film through etching using this resist film as a mask, the phosphorous doped polysilicon film 113a to 113c and 113 which has a predetermined pattern is formed as shown in FIG. 18. In this etching process, since the resist film is formed in the peripheral circuit region, the phosphorous doped polysilicon film 113 in the peripheral circuit region remains unchanged without being etched. After this, the resist film is removed. In this manner, the structure as shown in FIG. 18 is gained.
Next, a silicon oxide film is formed on the phosphorous doped polysilicon film 113a to 113c in the memory cell region and on the phosphorous doped polysilicon film in the peripheral circuit region by using a thermal oxidation method. The film thickness of this silicon oxide film is, for example, 5 nm. Next, a silicon nitride film is formed on this silicon oxide film by using a low pressure CVD method. The film thickness of the silicon nitride film can be made, for example, to be approximately 10 nm. Then, a silicon oxide film is formed on this silicon nitride film by using a low pressure VCD method. The film thickness of this silicon oxide film can be made, for example, to be approximately 5 nm. In this manner, a three layered insulating film made of a silicon oxide film, a silicon nitride film and a silicon oxide film is formed. As a result of this, the structure as shown in FIG. 19 is gained.
Next, a resist is applied to the three layered insulating film 115. Then, a resist film 128 is formed on the three layered insulating film 115 in the memory cell region through a photolithographic method. At this time, since the resist is removed from the peripheral circuit region, the three layered insulating film 115 is exposed in the peripheral circuit region. In this manner, the structure as shown in FIG. 20 is gained.
Next, the three layered insulating film 115 in the peripheral circuit region, the phosphorous doped polysilicon film 113 and the silicon oxide film 112 are removed through etching by using the resist film 128 as a mask. After that, the resist film 128 is removed. In this manner, the structure as shown in FIG. 21 is gained.
Next, as shown in FIG. 22, a silicon oxide film 129 is formed on the main surface of the semiconductor substrate 101 in the peripheral circuit region by using a thermal oxidation method. The film thickness of this silicon oxide film 129 is 15 nm. Here, in this thermal oxidation method, since a silicon nitride film forming the three layered insulating film 115 exists in the memory cell region, the phosphorous doped polysilicon film 113a to 113c located beneath this three layered insulating film 115 is not oxidized.
Next, as shown in FIG. 23, a phosphorous doped polysilicon film 116 is formed on the three layered insulating film 115 and on the silicon oxide film 129 both in the memory cell region as well as in the peripheral circuit region. This phosphorous doped polysilicon film 116 is formed by using a low pressure CVD method. In addition, the film thickness of this phosphorous doped polysilicon film 116 is 200 nm. A tungsten silicide film 117 is formed on this phosphorous doped polysilicon film 116. The film thickness of this tungsten silicide film 117 is 200 nm. Then, a silicon oxide film 118 is, further, formed on the tungsten silicide film 117.
Next, a resist film (not shown) which has a predetermined pattern is formed on the silicon oxide film 118 by using a photolithographic method. By partially removing the silicon oxide film 118 using this resist film as a mask, a silicon oxide film 118a to 118f (see FIG. 24) is formed. After that, the resist film is removed. Then, by partially removing the tungsten suicide (WSi) film 117 through etching using this silicon oxide film 118a to 118f as a mask, the tungsten silicide film 117a to 117f (see FIG. 24) is formed.
Then, by partially removing the phosphorous doped polysilicon film 116 using this silicon oxide film 118a to 118f as a mask, a phosphorous doped polysilicon film 116a to 116f is formed as shown in FIG. 24. The phosphorous doped polysilicon film 116a to 116d in the memory cell region functions as the control gate electrode of a flash memory cell. Then, the phosphorous doped polysilicon film 116e, 116f formed in the peripheral circuit region becomes the gate electrodes of the n type FET 126 and p type FET 127, respectively.
Next, a resist film 119 is formed, by using a photolithographic method, so as to cover the regions wherein the n type FET 126 and the p type FET 127 are to be formed in the peripheral circuit region. Under this condition, the three layered insulating film 115 and the phosphorous doped polysilicon film 113a to 113c are partially removed by using the silicon oxide film 118a to 118d as a mask in the memory cell region. In this manner, the structure as shown in FIG. 25 is gained. Through this etching, as shown in FIG. 25, a phosphorous doped polysilicon film 113ba, 113bb, 113bc, 113bd is formed to function as floating gate electrodes which are arranged at intervals in the direction perpendicular to the direction in which the word lines of the flash memory cells extend (direction in which the phosphorous doped polysilicon film 116a to 116d extend as control gate electrodes). In addition, another phosphorous doped polysilicon film 113a, 113c shown in FIG. 24 is divided in the same manner in the direction approximately perpendicular to the direction in which the word lines extend so as to be a phosphorous doped polysilicon film 113ab, 113cb as shown in FIG. 25. That is to say, the phosphorous doped polysilicon film 113ab, 113cb, 113ba, 113bb, 113bc, 113bd as the floating gate electrodes are in the condition arranged in a matrix form on the semiconductor substrate 101.
Then, in the memory cell region, arsenic ions are injected to the semiconductor substrate 101 which is located beneath the region wherein the upper surface of the silicon oxide film 112 is exposed. As for the conditions of this arsenic ion injection, the conditions where, for example, the injection energy is 40 keV and the injection concentration is 2.0xc3x971015/cm2 can be used. After that, a heat treatment is carried out by maintaining the semiconductor substrate 101 in a nitrogen atmosphere at a predetermined temperature. As for the conditions of this heat treatment, the conditions where the atmospheric temperature is 850xc2x0 C., heating time is 30 minutes, and the like, can be used. Through such a heat treatment the arsenic ions are activated. As a result of this, n type diffusion regions 120a to 120c are formed in the main surface of the semiconductor substrate 101 as shown in FIG. 26. In this manner, the structure as shown in FIG. 26 can be gained. After that, the resist film 119 is removed.
Next, a resist film (not shown) is formed, by using a photolithographic method, in a region other than the region where the n type FET 126 is to be formed. Under the condition where this resist film exists, arsenic ions are injected into the main surface of the semiconductor substrate 101 in the peripheral circuit region. As for the injection conditions, the conditions where the injection energy is 50 keV and the injection concentration is 3.0xc3x971015/cm2 can be used. After that, the resist film is removed. In addition, a resist film is formed in a region other than the region where the p type FET 127 is to be formed. Then, by using this resist film as a mask, BF2 ions are injected into the main surface of the semiconductor substrate 101 in the region where the p type FET 127 is to be formed. As for the conditions for this injection, the injection energy is 30 keV and the injection concentration is 3.0xc3x971015/cm2.
After that, the semiconductor substrate 101 undergoes heat treatment. As for the conditions for this heat treatment, the atmospheric temperature is 800xc2x0 C. and the substrate is maintained at this temperature for 30 min. Through this heat treatment, conductive impurities such as arsenic ions injected into the semiconductor substrate 101 in the peripheral circuit region are activated. As a result of this, n type diffusion regions 121a, 121b and p type diffusion regions 122a, 122b are formed. In this manner, the structure as shown in FIG. 27 is gained.
Next, boron phosphorous glass 123 (see FIG. 15) is formed on the silicon oxide film 118a to 118f by using a CVD method. The film thickness of this boron phosphorous glass 123 is 1000 nm. Then, by heat treating the semiconductor substrate 101, the boron phosphorous glass 123 is hardened. As for the conditions of this heat treatment, a nitrogen atmosphere is used as the atmosphere, the heating temperature is 850xc2x0 C. and the heating time is 30 min. A resist film (not shown) is formed on this boron phosphorous glass 123 by using a photolithographic method. By using this resist film as a mask, the boron phosphorous glass 123 and the silicon oxide film 112, 129 are partially removed through etching. In this manner, contact holes 124a to 124g (see FIG. 15) are created. After this, the resist film is removed. Then, by using a sputtering method, an aluminum-silicon-copper (Alxe2x80x94Sixe2x80x94Cu) alloy film is formed as a conductive film which extends from the inside of the contact holes 124a to 124g to the upper surface of the boron phosphorous glass 123. A resist film with an interconnection pattern is formed on this alloy film by using a photolithographic method. By using this resist film as a mask, the alloy film is partially removed through etching. After that, the resist film is removed. In this manner, interconnections 125a to 125g are formed as shown in FIG. 15.
In this manner, the conventional nonvolatile semiconductor memory device is produced.
In the above described nonvolatile semiconductor memory device according to the prior art, however, the below described problems arise. That is to say, a flash memory cell formed in the memory cell region has a so-called stacked gate structure wherein a floating gate electrode and a control electrode are layered. On the other hand, the n type FET 126 and the p type FET 127 in the peripheral circuit region are conventional field effect transistors, of which the gate electrodes do not have a stacked gate structure. Therefore, the silicon oxide film 112 as a tunnel insulating film in the memory cell region, the three layered insulating film 115 located on the phosphorous doped polysilicon film 113ab, 113bc, 113cb, 113ba, 113bc, 113bd and the silicon oxide film 129 as a gate insulating film formed in the peripheral circuit region are, respectively, formed through different process steps. As a result of this, the number of process steps of the nonvolatile semiconductor memory device increases leading to an increase in the manufacturing cost of the nonvolatile semiconductor memory device. Accordingly, the reduction of the manufacturing cost of semiconductor devices, such as a nonvolatile semiconductor memory device of which the manufacturing cost is relatively high, has become a particularly important problem to solve.
In addition, a current of a comparatively high voltage is necessary in order to carry out a write in operation, an erase operation, or the like, on a flash memory cell formed in the memory cell region. Therefore, the n type FET 126 and the p type FET 127 formed in the peripheral circuit region need to control a current of such a high voltage. Accordingly, a high level of dielectric strength is required for the silicon oxide film 129, which works as the gate insulating film of the n type FET 126, as well as for the p type FET 127, which are semiconductor elements in the peripheral circuit region, in order to control a current of such a high voltage.
The object of the present invention is to provide a semiconductor device and a nonvolatile semiconductor memory device of which the manufacturing processes are simplified so that the manufacturing costs can be reduced and at the same time, which have semiconductor elements that can control a high voltage as well as to provide the processes for the same.
A semiconductor device according to one aspect of this invention is a semiconductor device which has the first and the second semiconductor elements wherein the first semiconductor element includes a lower layer electrode formed on the substrate, an intermediate insulating film formed on the lower layer electrode and an upper electrode formed on the insulating film. The second semiconductor element includes a gate insulating film which is formed on the substrate and which is formed of the same layer as the intermediate insulating film and a gate electrode formed on the gate insulating film.
In this manner, as is made clear in the description of the process below, the intermediate insulating film of the first semiconductor element and the gate insulating film of the second semiconductor element can be formed in the same steps. Accordingly, the process of the semiconductor device can be simplified than in the case wherein the intermediate insulating film in the first semiconductor device and the gate insulating film in the second semiconductor element are formed in different steps. As a result of this, the manufacturing cost of the semiconductor device can be reduced.
In addition, by making the thickness of the insulating film, which forms the gate insulating film, sufficiently great, the dielectric strength of the gate insulating film can easily be increased. As a result of this, it becomes possible to control a comparatively high voltage in the second semiconductor element.
In the semiconductor device according to the above described aspect, the first semiconductor element may further include a lower insulating film which is formed beneath the lower electrode. The intermediate insulating film and the gate insulating film may have the film thickness larger than that of the lower insulating film.
In this case, the present invention can be easily applied to a nonvolatile semiconductor memory device such as a flash memory wherein it is necessary to arrange an insulating film of a comparatively thin film thickness as the lower insulating film. Then, in such a nonvolatile semiconductor memory device, it is necessary to control a high voltage in order to carry out the operations such as write in, erasing, or the like, of a memory cell. Therefore, by making the film thickness of the gate insulating film sufficiently large, the second semiconductor element can be effectively utilized as a semiconductor element for controlling such a high voltage.
In the semiconductor device according to the above described aspect, the intermediate insulating film and the gate insulating film may be formed of a plurality of insulating film parts.
In this case, it becomes possible to make the intermediate insulating film and the gate insulating film to have a multilayered structure wherein, for example, insulating film parts made of different materials are layered. Accordingly, by changing the material quality and the thickness of these insulating film parts, it becomes possible to arbitrarily change the electrical characteristics of the first and the second semiconductor elements. That is to say, it becomes possible to expand the scope of the electrical characteristics implemented in the first and the second semiconductor elements.
In the semiconductor device according to the above described aspect, the plurality of insulating film parts may include an oxide film, a nitride film arranged on this oxide film and an upper oxide film arranged on the nitride film.
In this case, the intermediate insulating film and the gate insulating film has a three layered structure of an oxide film, a nitride film and an upper oxide film. As a result of this, the dielectric strength of the gate insulating film can be increased without fail.
A nonvolatile semiconductor memory device according to another aspect of this invention is a nonvolatile semiconductor memory device comprising memory elements and peripheral circuit elements, wherein a memory element includes a floating gate electrode formed on the substrate, an intermediate insulating film formed on the floating gate electrode and a control gate electrode formed on the intermediate insulating film. Furthermore, a peripheral circuit element includes a gate insulating film, which is formed on the substrate and which is formed of the same layer as the intermediate insulating film, as well as a gate electrode formed on the gate insulating film.
In this manner, in the process of the nonvolatile semiconductor memory device, the intermediate insulating film of the memory elements and the gate insulating film of the peripheral circuit elements can be formed in the same steps. Accordingly, the process of the nonvolatile semiconductor memory device can be simplified in comparison with the case where the intermediate insulating film of the memory elements and the gate insulating film of the peripheral circuit elements are formed in separate steps. As a result of this, the manufacturing cost of the nonvolatile semiconductor memory device can be reduced.
In addition, by making the thickness of the gate insulating film sufficiently large, the isolation withstanding of the gate insulating film can easily be made larger. As a result of this, it becomes possible to control a comparatively high voltage in the peripheral circuit elements.
In the above described nonvolatile semiconductor memory device according to another aspect, the memory elements may further includes a tunnel insulating film formed below the floating gate electrode. The intermediate insulating film and the gate insulating film may have the film thickness larger than that of the tunnel insulating film.
In this case, the present invention can easily be applied to a flash memory, or the like, wherein it is necessary to arrange an insulating film of a comparatively thin film thickness as a tunnel insulating film. Then, in a nonvolatile semiconductor memory device such as the flash memory herein, it is necessary to control a current of a high voltage in order to carry out operations such as write in, erasing and the like of the memory cells. Then, by making the film thickness of the gate insulating film sufficiently large, the peripheral circuit elements which control such a high voltage can be easily implemented.
In the above described nonvolatile semiconductor memory device according to another aspect, the intermediate insulating film and the gate insulating film may be formed of a plurality of insulating film parts.
In this case, it becomes possible to make the intermediate insulating film and the gate insulating film to have a multilayered structure wherein, for example, insulating film parts made of different materials are layered. Accordingly, by changing the material quality and the thickness of these insulating film parts, it becomes possible to arbitrarily change the electrical characteristics of the memory elements and the peripheral circuit elements. That is to say, it becomes possible to expand the scope of the electrical characteristics implemented in the memory elements and the peripheral circuit elements in the nonvolatile semiconductor memory device.
In the above described nonvolatile semiconductor memory device according to another aspect, the plurality of insulating film parts may include an oxide film, a nitride film arranged on the oxide film and an upper oxide film arranged on the nitride film.
In this case, the intermediate insulating film and the gate insulating film has a three layered structure of an oxide film, a nitride film and an upper oxide film. As a result of this, the dielectric strength of the gate insulating film can be increased without fail. Accordingly, a peripheral circuit element which can control a current of a high voltage can be easily formed.
A process for a semiconductor device according to still another aspect of this invention is a process for a semiconductor device including the first and the second semiconductor elements, which includes the step of forming a lower electrode in the region where the first semiconductor elements are to be formed among the regions where the first and the second semiconductor elements are to be formed in the substrate, the step of forming an insulating film which extends from the lower electrode in the region where the first semiconductor elements are to be formed to the substrate in the region where the second semiconductor elements are to be formed, the step of forming a conductive film on the insulating film, the step of forming a resist film on the conductive film and the step of forming an upper electrode located on the insulating film in the region wherein the first semiconductor elements are to be formed and of forming a gate electrode located on the insulating film in the region wherein the second semiconductor elements are to be formed by partially removing the conductive film through etching by using the resist film as a mask.
In this manner, the intermediate insulating film located between the lower electrodes and the upper electrodes of the first semiconductor elements and the gate insulating film located below the gate electrodes of the second semiconductor elements can be formed of the above described insulating film. That is to say, the intermediate insulating film and the gate insulating film can be formed at the same time. Accordingly, a simplification of the process can be achieved in comparison with the case wherein the intermediate insulating film and the gate insulating film are formed in different steps, according to the prior art.
The above described process for a semiconductor device according to still another aspect may include the step of forming a lower insulating film which is located beneath the lower electrode in the region wherein the first semiconductor elements are to be formed and which has the film thickness thinner than the insulating film.
In this case, the present invention can be easily applied to a process for a nonvolatile semiconductor memory device such as a flash memory wherein it is necessary to provide an insulating film of a comparatively thin film thickness as a lower insulating film.
In the above described process for a semiconductor device according to still another aspect, the step of forming an insulating film may include the step of forming a first insulating film which extends from the lower electrode in the region wherein the first elements are to be formed to the substrate in the region wherein the second semiconductor elements are to be formed as well as the step of forming a second insulating film on the first insulating film.
In this case, it becomes possible to make the insulating film, which becomes the intermediate insulating film of the first semiconductor elements and the gate insulating film of the second semiconductor elements, have a multilayered structure wherein, for example, the first and the second insulating films made of different materials are layered. Accordingly, by changing the material quality or the thickness of these first and second insulating films, it becomes possible to arbitrarily change the electrical characteristics of the first and the second semiconductor elements.
In the above described process for a semiconductor device according to still another aspect, the first insulating film may be an oxide film while the second insulating film may be a nitride film. In addition, the step of forming the insulating film may further includes the step of forming an upper oxide film on the nitride film.
In this case, the intermediate insulating film and the gate insulating film have a three layered structure of an oxide film, a nitride film and an upper oxide film. As a result of this, the isolation withstanding of the gate insulating film can be increased without fail.
A process for a nonvolatile semiconductor memory device according to yet another aspect of this invention uses the above described process for a semiconductor device according to still another aspect.
Here, in a nonvolatile semiconductor memory device such as a flash memory, it is necessary to form memory elements and peripheral circuit elements for controlling these memory elements. Then, in a conventional process for such a nonvolatile semiconductor memory device, the gate insulating film of the peripheral circuit elements and the insulating film of the memory elements are formed in different steps. By applying a process for a semiconductor device according to the present invention, however, the memory elements correspond to the first semiconductor elements while the peripheral circuit elements correspond to the second semiconductor elements so that the insulating film located on the lower electrode of the memory elements and the gate insulating film of the peripheral circuit elements are formed at the same time as the same layer and, thereby, the process can be simplified.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.